1. Field of the Invention
The present invention relates to a method for manufacturing a low carbon ferrochrome with a high chromium content, and more particularly to a method for manufacturing ferrochrome which is added to a superalloy as a chromium source of a secondary component in the field of such superalloy as a nickel-based alloy, an iron-nickel-based alloy and a cobalt-based alloy.
2. Description of the Prior Art
High purity ferrochrome (containing 65 wt. % Cr or more) is added to a superalloy as a chromium source of a secondary component in the field of such superalloy as a nickel-based alloy, an iron-nickel-based alloy and cobalt-based alloy, and is indispensable for increasing corrosion resistance and the strength of superalloy. A great amount of high purity ferrochrome is used as a powdery additive material in the field of welding rod and powder metallurgy, the high purity ferrochrome being mixed with powdery iron or powdery nickel.
As the prior art methods for manufacturing high purity ferrochrome containing a high content of chromium, there are mainly, (a) the Perrin method, (b) the Swedish method, (c) the Multistage Perrin method and (d) other methods. Out of those methods, methods (a) and (b) are known as economical methods wherein high purity ferrochrome is manufactured in large quantities by the use of an electric furnace. The method (c) is a method wherein iron is removed from chromium ore under conditions of a weak reduction after a primary slag of chromium ore has been melted and low carbon ferrochrome is obtained by strongly reducing the secondary slag finally. In this method, low carbon ferrochrome having a high content of 85 to 90 wt. % Cr can be obtained. Further, the aluminium thermit method is considered as one of the other methods (d).
Chromium ore, which is economically available as a material, contains a high content of Fe. In consequence, in said Perrin method (a) and Swedish method (b), obtained is a a component of low carbon ferrochrome has the highest limit of 72 wt. % Cr. In the multistage Perrin method (c), ferrochrome having a high content of Cr can be obtained. There are difficulties in the multistage Perrin method (c) such that molten metal of a high melting point is hard to handle in a manufacturing process, that low carbon ferrochrome with a low content of Cr, which is produced in large quantities, is required to be processed, and that there are lots of impurities such as Si, O, N or the like in the product.